Lithium ion secondary batteries are widely used for small portable devices such as mobile phones and notebook computers. For a negative electrode material of the lithium ion secondary batteries, non-graphitizable carbon capable of doping (charging) and dedoping (discharging) of lithium in an amount exceeding the theoretical capacity of graphite of 372 mAh/g has been developed (see, e.g., Patent Document 1) and used.
Non-graphitizable carbon can be obtained by using, for example, petroleum pitch, coal pitch, phenolic resin, or plants as a carbon source. Among these carbon sources, plants are raw materials that can be sustained and stably supplied through cultivation, and are attracting attention because of being inexpensively obtainable. Since a carbonaceous material obtained by calcining a plant-derived carbon raw material has a large number of fine pores, favorable charge/discharge capacities are expected (e.g., Patent Documents 1 and 2).
On the other hand, due to the growing interest in environmental problems, lithium-ion secondary batteries are recently developed for on-board use and are coming into practical use.